Many brakes, for use on a vehicle, have an adjuster mechanism to set the position of friction elements to account for wear thereof. Generally, the adjuster mechanism has an adjuster shaft of which an end portion is accessible from the exterior of a brake housing and operable to manually re-wind or de-adjust the adjuster to permit removal and replacement of brake friction elements (commonly known as brake pads) and/or other servicing procedures. In conventional adjuster mechanisms having such a de-adjustment facility, there is a danger of excessive manual de-adjustment of the mechanism leading to locking together, shearing, or other damage to internal components thereof, resulting in the mechanism becoming inoperative in normal use.
An attempt has been made to solve this problem by providing a weakness or rupture in the adjuster shaft of such a mechanism so that shearing takes place at a predetermined excessive torque applied to the shaft in the de-adjustment and adjustment direction. This is disadvantageous in that the sheared shaft has to be replaced, requiring stripping and re-building of the adjuster after each shaft shearing.
An alternative solution is described in GB2304387, which provides a shearable or deformable element engageable with the shaft. The element shears or deforms when a torque above a pre-determined torque is applied (but less than the torque that damages the adjuster mechanism), so as to prevent or reduce further torque application to the shaft. However, this arrangement requires that the element be replaced after the element has deformed or sheared.